Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
1998-09-15
2001-10-16
Strecker, Gerard (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C324S236000, C324S252000, C324S260000, C324S327000, C324S345000, C324S249000, C235S449000, C331S065000, C360S110000, C360S326000
Reexamination Certificate
active
06304083
ABSTRACT:
BACKGROUND OF INVENTION
Materials known as Colossal Magneto-Resistive (CMR) or Giant Magneto-Resistive materials have been studied for their magnetic properties in both thin film and bulk forms. One such study, “Low-Field Giant Magneto-resistance at Microwave Frequencies”, Schmadel et al, Dept. of Physics and Center for Superconductivity Research, University of Maryland, College Park, MD 20742-4111, indicates that LBMO in the microwave frequencies may be useful in device applications. This presentation is representative of the research interest in the application of CMR materials to such devices as semiconductors and the like.
SUMMARY OF INVENTION
Magnetic sensors and methods using the sensors are used in a wide variety of applications. The sensors are used in such diverse applications as mapping the magnetic fields of the earth and security devices. There is a need for sensors that are low cost and accurate and that can be direct replacements for sensors in existing apparatus such as magnetometers. As described in the publication, “Giant magneto radio frequency absorption in magneto-resistive materials, etc., Frank J. Owens, J. App. Phys., 82 (6), Sep. 15, 1997, certain colossal magneto-resistance (CMR) materials can be used at and above room temperature for these purposes.
The invention is directed to measuring magnetic fields with sensors which have CMR materials that are ferromagnetic at temperatures that include from below about room temperature to about 370 degrees Kelvin. In one aspect it is in the form of apparatus such as sensors and systems which are combinations of sensors and external magnetic fields. The strength of the magnetic field is measured. In another aspect, it is methods and processes which use the sensors to determine the strength of external magnetic fields. The sensor contains at least one tunable, radio-frequency LC oscillator circuit. It has a frequency range which includes from about 1 KHz to about 10 MHz. A Colossal Magneto-Resistance (CMR) material is contained within the inductance coil of the LC circuit. This CMR material is ferromagnetic in a temperature range which includes about or above room temperature. It has a permeability sufficiently sensitive to external magnetic fields so that the presence of the field will produce a discernable change in the inductance of the LC circuit. This produces a corresponding change in the frequency of the LC oscillator. This frequency shift is correlated to the strength of the external magnetic field. An important aspect of the invention is that the strength of the magnetic field is measured by tuning with the LC circuit. Tuning of an LC circuit is recognized as one of the simplest and most accurate measurement techniques which are available. Therefore, the invention provides an accurate and simple apparatus and procedure to measure magnetic fields.
The methods and processes of the invention have the advantages that they can accurately measure low strength external magnetic fields, they can be practiced at ambient temperature without auxiliary cooling, and they are relatively inexpensive. This lends itself to mass production and systems using low cost sensors.
REFERENCES:
patent: 3239754 (1966-03-01), Odom, Jr. et al.
patent: 3416072 (1968-12-01), Fussell et al.
patent: 3443213 (1969-05-01), Bader et al.
patent: 4464691 (1984-08-01), Sawazaki et al.
patent: 5792569 (1998-08-01), Sun et al.
patent: 5872368 (1999-02-01), Osofsky et al.
Owens, Frank J., Giant magneto radio frequency absorption in magneto-resistive materials La0.7(Sr,Ca)0.3MnO3, J. Appl. Phys. 82 (86) pp 3054-3057. Sept. 15, 1997.
Beam Robert C.
Moran John F.
Sachs Michael C.
Strecker Gerard
The United States of America as represented by the Secretary of
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